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Physics Part II

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Class 10 Class 12
Water rises to a height 4.8cm in a certain capillary tube. When the same tube is dipped in some another liquid it falls by 12.5cm. Compare the surface tension of water and liquid. Density of liquid is 9.6 gm/cc and angle of contact of liquid is 120°.


Rise in water = 4.8 cm 
Fall in water when tube is dipped in some other liquid = 12.5 cm
Density of liquid = 9.6 gm/cc
Angle of contact of liquid = 120o

The height to which the liquid rises or falls in the capillary tube is given by the relation,

                        h=2T cosθrpg 

The above relation can be simplified to 

                        T=rgph2 cos θ                    ....(1)

Let T1 and T2 be the surface tension of water and liquid respectively.

By using the equation (1), we have


Here, ρ1=1 gm/cc,        h1=4.8cm,        θ1=0°         ρ2=9.6gm/cc,      h2=-12.5cm,   θ2=120°    T1T2=1×4.89.6×(-1.25)cos 120°cos 0°=15        


What is hydrostatics?

Hydrostatics is the branch of fluid mechanics that studies incompressible fluids at rest. The study of fluids at rest or objects placed at rest in fluids is hydrostatics.

What is hydrodynamics?

Hydrodynamics is the branch of science that studies about the force exerted by the fluids or acting on the fluids. 

Why solids have definite shape while liquids do not have definite shape?

Solids: Intermolecular forces are very strong and thermal agitations are not sufficiently strong to separate the molecules from their mean position. Solids are rigid and hence they have definite shapes.
Liquids: In liquids intermolecular forces are not sufficiently strong to hold the molecules at definite sites, as a result they move freely within the bulk of liquid, therefore, do not possess definite shapes. Liquids take the same shape as that of the container. 

Do intermolecular or inter-atomic forces follow inverse square law?

No. Intermolecular and inter-atomic forces do not obey the inverse square law. 

What is fluid?

Any material that can flow is a fluid. Liquids and gases are examples of fluid.